This invention relates to compression release engine brakes, and more particularly to simplified hydraulic circuits for such apparatus.
An illustrative portion of a conventional compression release engine brake 10 of the general type shown in such references as Cavanagh U.S. Pat. No. 4,399,787, Meistrick et al. U.S. Pat. No. 4,706,625, and Hu U.S. Pat. No. 5,201,290 (all incorporated by reference herein) is shown in FIG. 1. When the driver of the vehicle equipped with engine brake 10 wants the engine brake to operate, the driver closes vehicle dashboard switch 12 while fuel supply switch 14 is closed (signalling that the fuel supply to the internal combustion engine 100 associated with the engine brake is turned off) and while clutch switch 16 is also closed (signalling that the vehicle's drive train clutch is engaged).
When all of switches 12, 14, and 16 are thus closed, solenoid valve 30 is energized by current flow from vehicle battery 20 through fuse 22 and the above-mentioned switches. (Diode 24 helps prevent arcing when either of switches 14 and 16 opens.) When thus energized, solenoid valve 30 allows hydraulic fluid (typically engine lubricating oil) to flow through check valve 32 and conduit 34 into conduit 36. The hydraulic fluid in conduits 34 and 36 is generally at a relatively low pressure supplied by the lubricating oil circulating system of the engine. This relatively low pressure is sufficient to raise the spool 42 of control valve 40 to the position shown in FIG. 1 and to open the check valve 44 in that spool, as is also shown in FIG. 1. This allows low pressure hydraulic fluid to flow into conduit 50, slave piston cylinder 60, conduit 70, and master piston cylinder 80.
Before the engine brake is turned on, master piston return spring 84 holds master piston 82 up out of contact with the rocker lever linkage 110 that is disposed below master piston 82. (Rocker lever linkage 110 can be any suitable part of internal combustion engine 100 such as a fuel injector activating mechanism, an intake valve opening mechanism, or an exhaust valve opening mechanism of the engine.) However, when low pressure hydraulic fluid is supplied to master piston cylinder 80 as described in the preceding paragraph, the pressure of that fluid is sufficient to overcome the force of relatively weak spring 84, thereby forcing master piston 82 out into contact with rocker lever linkage 110 as shown in FIG. 1. Thereafter, each upward reciprocation of rocker lever linkage 110 causes master piston 82 to move upwardly, which causes a downward stroke of slave piston 62. Each downward stroke of slave piston 62 causes the slave piston to open at least one exhaust valve 120 in the engine cylinder associated with the slave piston. The timing of the upward strokes of rocker lever linkage 110 is such that exhaust valve 120 opens near top dead center of each compression stroke of the engine cylinder served by the exhaust valve. Accordingly, air compressed in that engine cylinder is released to the exhaust system of the vehicle and the engine does not recover the work of compressing that air during each subsequent "power" or expansion stroke of the engine cylinder. The engine therefore absorbs much more kinetic energy from the associated vehicle than it otherwise would, and the effectiveness of the engine in holding back or slowing down the vehicle is greatly increased. This prolongs the life of the vehicle's wheel brakes and improves vehicle operating safety.
The engine brake shown in FIG. 1 includes a so-called "reset" feature like that shown in above-mentioned Cavanagh U.S. Pat. No. 4,399,787. In particular, slave piston return stop screw 90 contains a vertically reciprocable plunger (not visible in FIG. 1, but an analogous plunger 224 is shown in FIG. 3 and described in more detail below). The bottom of the plunger initially covers the upper end of a vertical passageway 64a in slave piston 62. The lower end of passageway 64a communicates with a transverse passageway 64b in the slave piston. Transverse passageway 64b communicates with a branch 38 of conduit 36.
During each downward stroke of slave piston 62, the plunger in screw body 90 initially follows the slave piston down, thereby keeping passageway 64a closed. However, when the pressure in slave piston cylinder 60 drops to a certain level (because exhaust valve 120 has opened and the pressure in the associated engine cylinder has accordingly decreased), the plunger in screw body 90 is raised by an associated spring (not shown in FIG. 1 but analogous to spring 232 in subsequently described FIG. 3). This allows relatively high pressure hydraulic fluid to flow from slave piston cylinder 60 via passageway 64a/b, thereby allowing exhaust valve return spring(s) 122 and slave piston return springs 66 to produce a return stroke of slave piston 62. Such resetting of slave piston 62 prior to the return stroke of master piston 82 may be desirable for such purposes as ensuring that exhaust valves 120 are closed when the normal exhaust valve opening mechanism 130 of engine 100 next produces an exhaust valve opening. This avoids abrupt discontinuities in exhaust valve motion that could result from operation of mechanism 130 while exhaust valves 120 are already somewhat open due to downward displacement of slave piston 62.
The high pressure hydraulic fluid that escapes from the master piston/slave piston ("MP/SP") circuit when passageway 64a/b opens is accumulated under control valve spool 42, which is consequently displaced upwardly from the position shown in FIG. 1. This additional upward motion of spool 42 further compresses spring 46 and also compresses much stronger spring 48 in control valve 40. When master piston 82 subsequently performs its return stroke, the accumulated hydraulic fluid is immediately returned to the MP/SP circuit as a result of springs 46 and 48 forcing spool 42 down to the position shown in FIG. 1 and the concurrent opening of check valve 44.
When compression release engine braking is no longer desired, the driver of the vehicle opens switch 12. This de-energizes solenoid valve 30, thereby allowing hydraulic fluid to drain from conduit 36 via the bottom of the solenoid valve. When conduit 36 is thus de-pressurized, spring 46 urges control valve spool 42 down. This allows the MP/SP circuit to vent over the top of spool 42. With the MP/SP circuit thus vented, spring 84 can raise master piston 82 out of contact with rocker lever linkage 110. All compression release engine brake operations therefore cease.
Several variations of the apparatus shown in FIG. 1 are known. For example, above-mentioned Meistrick et al. U.S. Pat. No. 4,706,625 shows apparatus in which the slave piston reset mechanism is combined with a mechanism for automatically adjusting the "lash" (i.e., the cold-engine clearance C between the slave piston and the engine mechanism on which the slave piston acts during engine braking). Another known variation is the so-called "clip valve" which limits the downward stroke of the slave piston (e.g., by releasing high pressure hydraulic fluid as through passageway 64a/b after the slave piston has travelled down a predetermined amount). A form of such a clip valve is shown in above-mentioned Hu U.S. Pat. No. 5,201,290. Except for modifications of elements 62 and 90 (or modifications in the vicinity of those elements), all of these variations are typically constructed in the general way shown in FIG. 1.
From the foregoing it will be seen that, in systems of the various types described above, control valve 40 performs a relatively large number of functions. These are (1) providing a passageway for filling the MP/SP circuit, (2) isolating the MP/SP circuit from the low pressure portion of the circuit (e.g., conduit 36) during braking, (3) exhausting the MP/SP circuit when braking is no longer desired, (4) setting the minimum oil pressure in the MP/SP circuit for brake operation (i.e., as a result of the preload force in the spring of check valve 44 and in spring 46), (5) preventing premature movement of the slave piston (i.e. by movement of spool 42 up from the position shown in FIG. 1 to disconnect conduit 36 from conduit 50 in the event of excessive hydraulic pressure in conduit 36), and (6) accumulating hydraulic fluid temporarily displaced from the MP/SP circuit (e.g., when the above-described slave piston reset or clip valve operation occurs).
Control valve 40 is a relatively complex and expensive component of the engine brake. Moreover, the typical engine brake requires several such control valves. The control valves also tend to be a major contributor to high pressure leakage because high pressure hydraulic fluid from the MP/SP circuit can leak both upwardly and downwardly past spool 42 when it is in the position shown in FIG. 1. Such leakage tends to decrease the efficiency of motion transfer from the master piston to the slave piston.
In view of the foregoing, it is an object of this invention to improve and simplify the hydraulic circuitry of compression release engine brakes.
It is a more particular object of this invention to eliminate the control valves employed in compression release engine brakes such as those described above, while maintaining all the functionality provided by such valves.